1. Field of the Invention
The present invention relates to an image display system for displaying image information which is obtained by accessing an image data base or the like stored in an electronic filing device.
2. Related Background Art
In recent years, a number of apparatuses for handling image data of an electronic filing device and the like have been developed. An image display system shown in FIG. 4 for displaying the image information obtained from such a kind of apparatus has also been proposed.
FIG. 4 is a system block diagram for explaining the fundamental construction of a conventional image display system. Reference numeral 51 denotes an electronic filing device for managing images, documents, and the like of a large capacity which have been stored in a memory medium such as an optical disk or the like. Reference numeral 52 indicates a video RAM (VRAM) for storing image data read out of the electronic filing device 51. Reference numeral 53 represents a display which is constructed by, for example, a CRT for displaying images, documents, and the like on the basis of an image signal developed in the VRAM 52.
For use as the display 53, attention has been paid to a liquid crystal display different from a CRT display. Particularly, in association with the realization of a large screen, a display having a memory function of the active matrix type, ferroelectric type, or the like has been developed.
On the other hand, the electronic filing device has been being used for various kinds of processings such as identification and the like. Demand for executing various work by electronic processes by connecting a number of display terminals is becoming larger and larger.
However, the system for displaying image information through the VRAM 52 as mentioned above is constructed, for instance, as shown in FIG. 5.
FIG. 5 is a system block diagram for explaining a construction of a conventional image display system, in which the same parts and components as those in FIG. 4 are designated by the same reference numerals.
In the diagram, reference numerals 61-1 to 61-N denote terminal devices each comprising an interface IF, the VRAM 52, a keyboard KB, the display 53, and the like.
Therefore, the VRAM 52 needs to be individually provided for the terminal devices 61-1 to 61-N, so that there is a problem in that the system is very expensive.
On the other hand, even in the liquid crystal display having the memory function of the active matrix type, ferroelectric type, or the like, its memory function is insufficient. Consequently, there is also a problem in that the VRAM 25 is needed and the system is very expensive.
In addition to the above liquid crystal display, in the case where a page printer such as a laser beam printer (LBP) or the like is connected and image information is printed by the page printer, since the image data is transmitted to the page printer at a high speed, a page memory which is used only for the LBP is provided.
That is, as shown in FIG. 8, in a conventional image display system, an electronic filing device 81 or the like supplies image information to a VRAM 82 and a page memory 83, a display 84 receives an image signal from the VRAM 82, and an LBP 85 receives the image signal from the page memory 83. Namely, in the case of using the display 84 and LBP 85, two memories, the VRAM 82 and page memory 83, are needed.
Since the memory construction of the VRAM 82 only for use of the liquid crystal display, and that of the page memory 83, only for use in the LBP are almost the same, there is a demand for being able to use first one video RAM by commonly constructing the memories 82 and 83.
However, in such case, when a signal of the video RAM is being output to the LBP 85, it cannot be displayed by the liquid crystal display 84; and on the other hand, when a signal of the video RAM is being output to the liquid crystal display 84, it cannot be output by the LBP 85.